Introduction

Imagine yourself floating helplessly on the open sea, thousands of miles from land, your destination at the mercy of the wind and currents. Perhaps eventually you may drift ashore on the coral sand beaches of a remote tropical island or distant continent. This is precisely what happens to countless thousands of tropical drift seeds and fruits, a remarkable flotilla of flowering plants that travel the oceans of the world. The following map shows the path of some drift seeds and fruits in the world's oceans:

Seeds provide the vital genetic link and primary dispersal agent between successive generations of plants. They are produced and packaged in botanical structures called fruits, and come in an endless variety of shapes and sizes. Tropical drift seeds and fruits are especially remarkable because they can survive months or even years at sea. They are very buoyant, with thick protective shells which are impervious to salt water. In some drift fruits, such as the coconut, the seed embryo and fleshy white "meat" (endosperm) is enclosed within a hard, bony layer (endocarp) surrounded by a thick fibrous husk. Other drift seeds have thick woody seed coats and internal air cavities which produce their buoyancy. During their long voyages they often cross entire oceans, perhaps colonizing the shores of a coral atoll or isolated volcanic island. Sea dispersal is a hit-or-miss method; after a long, perilous journey, other dangers await the vulnerable seedlings. They may perish in the parched sand without adequate moisture or be quickly devoured by ravenous land crabs. Drift seeds carried by the Gulf Stream from the Caribbean to beaches of northern Europe may find themselves in another precarious situation--aliens in a hostile climate much too cold for them to survive.

The tropical islands of Indonesia, Polynesia and the Caribbean
probably have the greatest variety of drift seeds. They are especially
abundant along wave-swept beaches following the hurricane season, and may
be carried inland by tidal waters. The Cayman Islands and Yucatan
Peninsula lie directly in the path of the Equatorial Current, bringing
thousands of unique drift disseminules from the Amazon and Orinoco deltas
and across the Atlantic from river deltas of tropical west Africa. In the
Pacific region drift seeds may be deposited well above the inhospitable
beach zone by enormous tidal waves known as tsunamis. The tsunami emanates
from an earthquake or volcano epicenter and moves at great speed across the
Pacific Ocean.

Drunk Bay on the windward side of the island of St. John in the U.S. Virgin Islands. The following variety of drift seeds and fruits came from Drunk Bay. They were collected along the beach and rocky shore shown in the above photo in approximately three hours.

Drift seeds and fruits collected at Drunk Bay on the island of St. John. Many of these disseminules are discussed in the following paragraphs.

"Nothing nut" (Cassine xylocarpa) on the leeward shore of St. John in the U.S. Virgin Islands. The common name is derived from the Creole name of "not'ing nut," so called because no useful purpose is known for the "nuts" of this endemic shrub. This shrub (or small tree) is also called "marble tree" because of the hard, woody, seed-bearing endocarps. Cassine (syn. Eleodendron) is a member of the staff tree family (Celastraceae). The genus includes the Asian false olive (C. orientalis), the African C. capensis, the Australian C. australis, the Bermudian C. laneana, and the Cuban C. attenuata.

Charles Darwin & Ocean Dispersal Of Seeds

Plant dispersal by ocean currents has fascinated many famous
explorers, including Charles Darwin and Thor Heyerdahl. Sea currents have
also been studied by the U.S. Coast and Geodetic Survey using stoppered
bottles containing a numbered postcard. When a bottle is found on a beach
the finder fills out the card and drops it in the mail. It takes about one
year for a drift bottle to float from Yucatan to Ireland. A bottle
launched near Caracas, Venezuela reached the Florida Keys four months
later, traveling at an average speed of 16 statute miles per day. It is
estimated that tropical seeds found on European shores probably have been
adrift for a year or longer.

During his famous voyage around the world on the H.M.S. Beagle,
Charles Darwin championed the idea of drift seeds and fruits colonizing
distant islands, particularly isolated volcanic islands which have never
been connected to the mainland. Darwin studied the role ocean currents played in the flora of Cocos Keeling Islands in the Indian Ocean, and concluded that most of the endemic vascular flora was derived from drift seeds and fruits. His original article published in 1836 was reprinted in chapter 20 of Journal of Researches, D. Appleton & Company, New York, 1883.

After he returned to England, Darwin
conducted flotation experiments with cultivated plants. In the Journal of the Proceedings of the Linnaean Society (Vol. 1, 1857) Darwin stated: "I soon became aware that most seeds, in accordance with the common experience of gardeners, sink in water; at least I have found this to be the case, after a few days, with the 51 kinds of seeds which I have myself tried; so that such seeds could not possibly be transported by sea-currents beyond a very short distance." Darwin also mentioned rafting as a dispersal mechanism for seeds that generally don't float well in sea water. In addition, he stated that seeds contained within pods, capsules and the heads of Asteraceae may be carried by ocean currents and washed ashore on distant beaches. In his Origin of Species, 1859 (Chapter 12 Geographical Distribution: Means of Dispersal), Darwin summarized his experimental data on seed dispersal in salt water, and expressed a higher confidence in dried seeds: "Therefore it would perhaps be safer to assume that the seeds of about 10/100 plants of a flora, after having been dried, could be floated across a space of sea 900 miles in width, and would then germinate."

Of all the 250,000 species of seed plants on earth, only about 250
species (0.1 percent) are commonly collected as drift disseminules on
tropical beaches; and only about half of these are known to produce seeds
that can float in seawater for more than a month and still be viable. This
relatively small number of drift seed species does not include seed plants
which are dispersed on vegetation rafts, drift garbage from ships, or true
marine seagrasses which live totally submersed in seawater. Although the
total number of drift seed species with long viability periods may be relatively small, they nonetheless
form a floral flotilla comprising countless thousands of individuals riding
the ocean currents of the world.

The Hawaiian archipelago has been isolated from continental land masses during the past 30 million years, and yet the 1,000 species of indigenous Hawaiian angiosperms are believed to stem from natural introduction by long-distance dispersal of 280 ancestral plant colonists (Wagner, Herbst and Sohmer, 1990). According to Sherwin Carlquist (Hawaii: A Natural History, 1980), only about 14 percent of the original flowering plant immigrants to the Hawaiian Islands are clearly adapted to oceanic drift. If dispersal by birds and air currents are ruled out, it appears that seeds were carried thousands of miles to these islands, possibly by rafting or within protective capsules and pods. For example, California tarweeds are not included with tropical drift seeds, and yet an ancestral tarweed traveled at least 3,000 miles to the Hawaiian Islands where it gave rise to a remarkable group of endemics known as the "Silver Sword Alliance." The small seeds from ancestral members of the lobelia family (Campanulaceae) also reached these islands giving rise to an unusual group of Hawaiian lobelioids. One of these is the pachycaul Brighamia insignis that grows on steep sea cliffs on the island of Kauai.

An interesting coral tree endemic to dry, leeward slopes of all the
main Hawaiian islands is called wiliwili (E. sandwicensis). This Hawaiian endemic belongs to
a group of closely related passerine species in the section Erythraster,
including E. tahitensis, endemic to Tahiti; E. variegata, a widespread
species in tropical Asia and the South Pacific; and E. velutina, another
widespread species in northern South America, the West Indies and the
Galapagos Islands. Although the seeds of wiliwili sink in water, it may
have originated from an ancestral species with buoyant seeds that
reached these islands many thousands of years ago. In fact, a related
tropical Asian species (E. variegata), which is commonly planted as a
street tree in Hawaii, has seeds that float in water. The seeds of this
species sometimes show up along Hawaiian beaches and tidal waters;
however, they are usually of local origin. Trees of E. variegata are
fairly easy to identify because the pods are longer than most cultivated
coral trees, often up to 12 inches or more in length.

According to Sherwin Carlquist (1980),
the seeds of wiliwili (Erythrina sandwicensis) have gradually lost their
ability to float in seawater. Although the reasons are not identical,
Carlquist compares this with the loss of flight in certain insects and
birds. "If a plant shifts its ecological preference, it will tend to
lose contact with the agent responsible for its dispersal."

Seeds of the Asian coral tree (Erythrina variegata) are buoyant in seawater and may have drifted to distant shores of the tropical Pacific. In fact, this species (or its progenitor) may have given rise to several species of endemic coral trees in the tropical Pacific region.

The Hawaiian Silver Sword

The Hawaiian islands are
thousands of miles from the nearest continent or island mass. Even though they include some of the most isolated islands on earth, they contain numerous endemic species of plants, many of which evolved from ancestral seeds that reached the islands by drifting. Some striking members of the sunflower family evolved on the Hawaiian Islands from an ancestral California tarweed (Hemizonia) that colonized these isolated Pacific islands millions of years ago. This group of plants, called the Silver Sword Alliance, includes three genera and about 30 endemic species, an excellent example of adaptive radiation. One of the most amazing of all these Hawaiian endemics is the silver sword (Argyroxiphium sandwicense ssp. macrocephalum) that only grows in the cinders of Haleakala Crater on the island of Maui. The rosettes of sword-shaped leaves are covered with silvery hairs that reflect light and heat and provide insulation against the intense solar radiation and extreme aridity of this 10,000 foot (3,000 m) volcanic mountain.

A silver sword (Argyroxiphium sandwicense ssp. macrocephalum) in full bloom inside the lunar-like crater of Haleakala on the island of Maui. This remarkable plant and its relatives are descendents of an ancestral California tarweed (Hemizonia) that reached these islands millions of years ago, presumably by drifting.

Nickernuts

Some of the most ubiquitous drift seeds that readily germinate on
tropical beaches are the gray and yellow nickernuts, Caesalpinia bonduc, C. ciliata,
C. major. All are climbing, sprawling beach shrubs armed with vicious,
recurved thorns and prickly pods bearing gray or yellow seeds. The smooth,
marble-like seeds are commonly strung into necklaces and bracelets, often
mixed with other colorful seeds. In Guayaquil, Ecuador, drilled nickernuts
are sold by street vendors as amulets to ward off evil spirits. On some
Caribbean islands nickernuts are used in a strategy board game called
"Island Waurie." Two players sit on opposite sides of a hardwood board
with six depressions (wells) on each side, each well with four nuts.
Through a series of carefully planned moves, players attempt to empty all
six of their wells before their opponent can do so. Legend has it that
Island Waurie was originally introduced to the Cayman Islands by Blackbeard
the Pirate on one of his voyages from South Africa. The game became
popular with Cayman Islanders and was enjoyed by Ernest Hemingway whenever
he visited the islands. Know in Africa as "mancala," the games were played
for thousands of years in Egypt, where boards have been found carved into
the stone of the pyramid of Cheops and the temples at Luxor and Karnak.

The Coconut

Probably the best known of all plant drifters is the coconut (Cocos
nucifera). In fact, it is hard to imagine a tropical beach without coconut
palms. The origin of the coconut and whether it floated to islands of the
tropical Pacific has been debated for more than a century. T.H. Everett
(Encyclopedia of Horticulture, Vol. 3, 1981) flatly states: "...it has
never been found truly wild, every coconut palm is planted by man or
derived from such a planting." According to the world authority on palms,
E.J.H. Corner (The Natural History of Palms, 1966), "There is no island or
shore where its presence is not due directly or indirectly to its having
been planted by man." Probably under most situations, coconut seedlings
require watering and other attention from humans; however, J.V. Dennis and
C.R. Gunn (Economic Botany 25, 1971) cite several localities where coconuts
appear to have seeded themselves naturally, including cays in British
Honduras (Belize), rocky islets in the Fiji group, the east coast of
Trinidad, Cocos-Keeling Atoll in the Indian Ocean, and Krakatau and
adjacent islets following the catastrophic eruption of 1883. In addition,
I have photographed coconut palms sprouting on Tetiaroa Atoll in French
Polynesia. Whether these would survive the ravaging effects of land crabs
and intense sunlight and grow into mature palms is hard to say, but there
appeared to be palms of different ages along the beaches. I have also
observed self-seeded coconut palms growing among mangrove thickets on cays
off the coast of Belize.

The end of a long journey: Box fruits (Barringtonia asiatica) and a sprouting coconut (Cocos nucifera) on the coral sand beach of Tetiaroa Atoll, French Polynesia.

Hugh C. Harries (Botanical Review Vol. 44, 1978) argues convincingly
that coconuts have naturally established themselves on beaches of the
tropical Pacific. According to Harries, there are many varieties of
coconuts, but they all belong to either of two major types known as niu kafa and niu vai. The niu kafa types have an elongate, angular fruit, up to 6 inches in diameter, with a small egg-shaped nut surrounded by an
unusually thick husk. Niu vai types have a larger more spherical fruit, up
to 10 inches in diameter, with a large, spherical nut inside a thin husk.
The niu kafa type represents the ancestral, naturally-evolved, wild-type
coconut, disseminated by floating. The niu vai type was derived by
domestic selection for increased endosperm ("meat" and "milk") and is
widely dispersed and cultivated by humans. Both types of fruit can float,
but the thicker, angular husk adapts the niu kafa type particularly well to
remote atoll conditions where it can be found today. The presence of
"undesirable" wild-type coconuts growing in mangrove swamps is clear
evidence that they were self-sown and not planted by farmers. In two
fascinating papers by Harries and his colleagues, W.S. Gruezo and R.
Buckley (Biotropica Vol. 16, 1984), wild-type, self-sown coconuts have been
documented in the Philippines and as far away as Australia. In addition,
throughout the humid tropics intermediate types have arisen by
hybridization with the commonly cultivated niu vai coconuts.

Angular, small-seeded coconuts on Ambergris Caye, off the coast of Belize. These coconuts resemble the wild-type niu kafa coconuts discussed by Harries and his colleagues. They were probably introduced to the Caribbean region of Central America by Portuguese traders.

The argument for a New World origin of the coconut centers around the
presence of coconut palms on Cocos Island off the coast of Costa Rica and
parts of the Pacific Coast at the time of Columbus. One of the proponents
of the New World origin is Thor Heyerdahl, citing his own experience on the
Kon Tiki and legends handed down by early Polynesian voyagers. In his
book, Sea Routes to Polynesia (1968), Heyerdahl expresses great confidence
in Polynesian sailors who crossed vast stretches of the Pacific Ocean
carrying staple foods from the New World, such as sweet potato, plantain
and the coconut.

A major factor in Hyerdahl's argument comes from the distribution of the sweet potato (Ipomoea batatas). Archaeological evidence shows that sweet potatoes were cultivated in South America by 2400 B.C. and fossilized sweet potatoes from the Andes have been dated at 8,000 to 10,000 years old. Although the sweet potato is clearly native to South America, it was cultivated in Polynesia as early as 1200 A.D. In fact, the sweet potato had already become the principle food of the Maoris in New Zealand by the time of Captain Cook's historic voyage to that part of the world in 1769. It is interesting to note that the sweet potato is known as "kumar" or "kumal" in the Lima region of coastal Peru, and it is called "kumara" by the Maoris of New Zealand. Heyerdahl (1968) postulated that sweet potatoes were carried across the Pacific by Peruvian Indians before Europeans began to sail the world's oceans. He tested his hypothesis in 1947 by sailing a balsa wood raft, the Kon-Tiki, fashioned after the reed rafts of the Oru Indians living on Lake Titicaca in Bolivia. Although Heyerdahl's hypothesis about the transoceanic exchange of sweet potatoes by skillful pre-Columbian sailors remains an enigma (at least to some skeptics), his New World origin for the coconut has been rejected by most botanists.

According to J.V. Dennis and C.R. Gunn (Economic Botany 25, 1971), the coconut is indigenous to the Indo-Malaysian region. It spread by sea currents to many Pacific Island groups with adequate rainfall and moderate temperatures where the seedlings became established along beaches. Coconuts prefer the well-drained coral sand beaches of tropical
islands and atolls, and are poorly established along shores of continents.
In a recent article by F. Rosengarten, Jr. (Principes 30, 1986), naturally
dispersed coconuts can withstand occasional brief salt water flooding.
Developing coconut palms obtain fresh water and mineral nutrients from a
lens (soil layer) of fresh water (derived from island rainfall) which
literally floats above the denser salt water beneath the beach sand.

According to Dennis and Gunn, 3,000 miles seems to be the average
maximum distance that a coconut will remain afloat and still remain viable.
These limitations greatly diminish the chance of a coconut reaching the New
World, let alone sprouting on a continental shore. Most authorities agree
that the coconut was introduced to the New World by Portuguese and Spanish
traders. Although the coconut is the best known drift fruit it is also one
of the world's most valuable trees, providing thatching, food, drink, coir,
copra, oil, and hard endocarps which are fashioned into all sorts of
decorative and useful articles.

Coconut on a beach in Belize.

The origin of the generic name for coconut "Cocos" may be traced to the three germination pores on the endocarp layer surrounding the seed. According to R. Sokolov (Natural History Oct. 1989), Portuguese and Spanish traders introduced the coconut into West Africa after 1500. They called it "coco" from the Portuguese or Spanish slang word for monkey face, supposedly because of the eye pattern on the endocarp and the brown, fibrous hair (husk). Coconuts were later introduced into the Americas by these early traders. The center of origin for ocean-dispersed coconuts appears to be the Indo-Malaysian region.

Perhaps the best physical evidence for an Indo-Pacific origin of the
coconut comes from New Zealand and India, where fossil specimens of a
species of Cocos have been dated to the late Tertiary, at least two million
years ago. According to Hugh Harries (Principes Vol. 36, 1992), fossil
coconuts of an extinct Miocene palm (Cocos zeylandica) have been found in
North Island, New Zealand. Fossil evidence from such far-flung areas
suggests that the coconut had ample time to disperse naturally in the Indo-Pacific, before humans came along to speed up the process.

But of all the arguments for a transoceanic dispersal of coconuts,
perhaps the most interesting comes from the widespread distribution of the
coconut crab (Birgus latro). According to Harries (Principes Vol. 27,
1983), this large land crab could not have achieved its present widespread
inter-island distribution with only a 30 day aquatic larval stage unless
they rafted to distant islands. Harries postulates that the tiny post-larval (glaucothoe) stage was spent in the moist husk of floating coconuts.
Ancestors of today's coconut crabs may have literally migrated on floating
coconuts to remote islands and atolls of the South Pacific.

The widespread distribution of the coconut crab (Birgus latro) coincides with coconut palms throughout the tropical Pacific region. The post-larval stage of these crabs may have actually rafted on coconuts from island to island.

The Galapagos Islands

The Galapagos Islands, always a provocative place for students of natural history, offer a wide variety of examples of drift dissemination, including the independent transport of seeds and fruits floating in the ocean and the transport of seeds and animals on vegetation rafts from the mainland. Several species of mangroves grow on these islands, including the ubiquitous red mangrove (Rhizophora mangle) with its conspicuous prop or stilt roots descending from its limbs. The cigar-shaped disseminule, known as a "sea pencil," is unusual because it is a germinated seedling and not a seed or fruit. The seedling, with its long, pendant taproot (mostly hypocotyl), drops from the parent plant, where it may be automatically planted in the mud of shallow water or washed away to a distant shore. Beach vines, such as beach morning glory (Ipomoea pes-caprae), gray nickernut (Caesalpinia bonduc) and beach bean (Canavalia maritima), occur on several of the islands. Their durable seeds ride the currents of the world's oceans, resulting in enormous pantropic distributions.

Beach bean (Canavalia maritima). This trailing and climbing vine is common
on tropical beaches of Central and South America, and along the shores of many Caribbean islands.

Ian Thornton, a zoologist at La Trobe University in Melbourne, Australia, has calculated that, based on the speed of the currents and winds of the area, it would take about two weeks for a floating log or vegetation raft to reach the Galapagos Islands from mainland Ecuador. Considering that the archipelago is over 3 million years old, the drift seed scenario offers a plausible explanation for how some plants made the 600-mile (965-km) journey.

Successful dissemination by drifting would not have to occur often for it to have a profound effect on the ecology of the islands. Taking into account all methods of dispersal, including transport by wind, birds, and drifting on the ocean surface, Duncan Porter, a botanist at Virginia Polytechnic Institute and State University, estimates that 378 original introductions could account for the 522 indigenous plant species known to grow on the islands. Of these natural introductions, 59% were a result of transport by birds, 32% by wind transport, and 9% by drifting on the ocean surface. If only one species successfully drifted to the islands and germinated there every 50,000 years, this would still account for the introduction of roughly 10 percent of the islands's flora. According to D.M. Porter (Nature Vol. 264, 1976), for 378 introductions to account for the present flora, it would require only one species to arrive and become established every eight to ten thousand years.

Ancestors of present-day Galapagos reptiles, such as the remarkable marine iguanas, may have also drifted to the islands. In the swift current of Ecuador's Guayas River, trees, branches, and large mats of vegetation broken loose from riverbeds are commonly carried out to sea. Reptiles now on the Galapagos may have ridden such rafts from the mainland many thousands of years ago. For example, in 1827 a large boa constrictor reportedly arrived on the island of St. Vincent in the West Indies, wrapped around the trunk of a floating tree.

A marine iguana (Amblyrhynchus cristatus) on the rocky shoreline of Hood Island in the Galapagos Archipelago. These unusual sea-dwelling iguanas are descendants of an ancestral mainland species that rafted to these islands thousands of years ago. In the distance is the infamous M/N Bucanero.

The Pantropical Mangroves

Mangroves include several dozen species of trees and shrubs that grow along tidal swamplands throughout tropical regions of the world. Since their roots are emersed in water-logged silt and mud, often
deficient in oxygen, the buttressed trunks and aerial roots of mangroves are
typically dotted with numerous lenticels--small pores which provide gas
exchange between the roots and the atmosphere. Lenticels are especially
conspicuous on the prop roots of the ubiquitous red mangrove (Rhizophora mangle) and on the deeply-fluted trunk of the tea mangrove
(Pelliciera rhizophorae), an interesting swamp tree of the tea family
(Theaceae) along the Pacific coast of Costa Rica. The lateral roots of some mangroves produce upright, slender outgrowths called pneumatophores which extend above the mud and water like snorkel tubes. The porous pneumatophores are covered with lenticels and provide additional
aeration for the root systems. The black mangrove (Avicennia germinans), of Central America and the Caribbean region, produces literally hundreds of pencil-like pneumatophores around its base.

Mangroves survive in seawater with a salinity that would be lethal to most trees and shrubs. Like celery or
carrot sticks placed in saltwater, the roots of most plants rapidly lose
water if they are suddenly emersed in seawater. Halophytes (salt-loving
plants), such as mangroves, generally have a lower concentration of water
molecules (lower water potential) in their root cells so they can take in
water. They maintain lower water potentials in their roots by having
higher internal salt concentrations than seawater and by losing water at
the leaf surface. Since high internal salt concentrations can be lethal to
plant cells, some species such as the black mangrove and white mangrove
(Laguncularia racemosa), can excrete excess salt through special
glands in their leaf blades and petioles. Red mangroves have root cell membranes which prevent the absorption of excess salt.

The seeds of mangroves are especially remarkable because they commonly germinate within their fruit while still attached to the parent plant, a condition known as "viviparous seeds." Having their embryonic root
(hypocotyl) already elongated gives them a better chance of establishing
themselves in soft mud during low tide. Called "sea pencils," the cigar-shaped seedlings (disseminules) of red mangrove may have an elongate taproot up to 10 inches long when they drop from the parent tree. The unusual, top-shaped fruit of tea mangrove contains one of the largest seeds in the world (excluding palms). It floats with the elongate, embryonic root
pointing downward, and readily becomes implanted in soft mud. Germinated seedlings and sprouted fruits of the black mangrove and white mangrove are also dispersed by ocean currents.

Left: Red mangrove (Rhizophora mangle) with two viviparous (germinated) seedlings which have emerged from their fruits. The elongate embryonic axis called the hypocotyl develops into an extended taproot; Center: Onion-sized fruits of the tea mangrove (Pelliciera rhizophorae). The pointed beak encloses the embryonic root (hypocotyl). The fruit floats with the beak facing downward. When it becomes stranded in shallow water at low tide, the beak becomes implanted in the soft mud or silt, thus fascilitating the establishment of the seedling; Right: A sprouted fruit of black mangrove (Avicennia germinans) showing an elongated root.

Red mangrove (Rhizophora mangle) with a viviparous (germinated) seedling still attached to the fruit on the parent shrub. The seedling drops into the water where it is automatically planted in the soft mud or floats away.

Polynesian Box Fruit

Beaches of French Polynesia are often littered with a buoyant drift
fruit resembling a small coconut with flattened sides. It is called box
fruit (Barringtonia asiatica) and is one of the most durable and widespread
of all drifters, remaining buoyant for at least two years. In fact, they
are used as fishing floats in Southeast Asia. This was one of the first
tropical drifters to reach Krakatau after the catastrophic volcanic
eruption of August 1883.

Box fruits (Barringtonia asiatica) are widespread drift fruits in the tropical Pacific, remaining buoyant for more than two years. They are common in the turquoise-blue waters of French Polynesia.

Polynesian Tamanu

An equally common drift fruit of the tropical
Pacific is called "tamanu" (Calophyllum inophyllum) by the Polynesians.
The smooth, gray fruits resemble ping-pong balls strewn along wave-swept
beaches. This tree belongs to the garcinia family (Clusiaceae syn. Guttiferae). On Marlon Brando's spectacular atoll of Tetiaroa, strings of
tamanu balls on fishing line are used for decorative "lamp shades."
Another common drifter, called tropical almond (Terminalia catappa),
resembles an oversized unshelled almond. It is one of the most distinctive
trees of tropical beaches with tiered, pagodalike limbs and colorful red
and yellow leaves reminiscent of a deciduous forest in autumn. Seeds of
the Polynesian "tianina" or lantern tree (Hernandia nymphaeifolia) are
produced in fleshy red or white "lanterns" which float like colorful boats
in the clear blue water. The woody, seed-bearing endocarps are polished by
native islanders and made into shiny brown leis and necklaces.

The smooth, ping-pong ball fruits of tamanu (Calophyllum inophyllum) commonly drift ashore on beaches of French Polynesia. On the atoll of Tetiaroa they are strung on fishing line to make unusual lamp shades.

Flowers of tamanu (Calophyllum inophyllum). The stamens occur in five bundles. On the small East-Indonesian island of Alor, this pantropic tree is called "camplung." Here the sticky seed within the dried pericarp is used for lighting. It burns with a clean flame and reportedly fends off mosquitoes. According to S. Facciola (Cornucopia II, 1998) the ripe fruits and seeds are edible. According to C.R. Gunn and J.V. Dennis (World Guide to Tropical Drift Seeds and Fruits, 1976), this is one of the first trees to colonize newly formed Islands in the Pacific region.

The Polynesian Pandanus

Another widespread Polynesian plant called screw pine (Pandanus tectorius) is also dispersed by ocean currents. The large multiple fruit (resembling a pineapple) is composed of buoyant, one-seeded sections called "keys." The hard, woody keys are also polished and made into necklaces and leis.

The multiple fruit of Pandanus tectorius, showing the individual one-seeded sections called "keys." In addition to the edible seeds (one inside each key), the keys are polished and used for necklaces and leis. The keys are very buoyant and water-resistant, and remain viable for months. They are dispersed by ocean currents to shores of distant atolls and islands throughout the tropical Pacific.

Sea Beans

Some of the most beautiful of all drift seeds are called "sea beans."
They come from large climbing vines (called lianas) throughout rain forests
of the New and Old World tropics. The seeds are produced in large pods and
resemble round, flattened beans with hard, woody seed coats. In species of
Mucuna the pods are covered with whiskerlike, stinging hairs--presumably to
discourage ravenous seed predators. The pods develop from clusters of
greenish, bat-pollinated blossoms at the end of long, ropelike branches
which hang from the forest canopy. Sea beans are also called "hamburger
seeds" because they have two rounded halves enclosing a conspicuous central
connection layer (hilum). In Mexico and Central America they are also
called "ojo de buey" because of their uncanny resemblance to the eye of a
steer. Another species of sea bean (M. argyrophylla) called "ojo de
venado" (deer eyes) has a most remarkable use in Central America.
According to the Flora of Guatemala by P.C. Standley (Fieldiana Vol. 24,
1946), "male" and "female" seeds from this rain forest liana are carried by
natives to prevent hemorrhoids. The sex of the seed is determined by
whether they sink or float in water. Those that sink in water are called
"hembras" (female) and those that float are "macho" (male). The
hemorrhoidal treatment requires the sufferer to carry a "male" and a
"female" seed in their back pocket. Some species of sea beans are called
sea purses (Dioclea) because they are shaped like a purse, including a
circular hilum along the edge that superficially resembles a zipper.

Velvety pods of the sea bean (Mucuna argyrophylla) hang from long, ropelike stems in the rain forests of Belize. The hard, black seeds are called "ojo de buey" (eye of the steer) and "ojo de venado" (eye of the deer) by local residents.

The Sea Heart

Perhaps the most remarkable of all drift seeds resemble large wooden
hearts and are called "sea hearts" (Entada gigas). The heart-shaped seeds
are produced in huge bean pods up to six feet long, the longest of any
legume. In the rain-soaked tropical forest near Golfito, Costa Rica,
enormous sea heart lianas twine through the forest canopy like a gigantic
botanical boa constrictor. The vine is known locally as "escalera de mono"
or monkey ladder because it provides a maze of arboreal thoroughfares for
New World monkeys. Torrential rains wash the seeds into streams and rivers
where they reach the sea, and perhaps eventually the shores of a distant
continent. Sea hearts are highly prized by beach combers and make
beautiful pendants when polished. Sea hearts and a similar rectangular Old
World species (E. phaseoloides) were commonly used in Norway and northern
Europe for snuffboxes and lockets. The seeds were cut in half, the
contents removed, and the woody seed coats hinged together.

Sea hearts have a long and colorful history in fact and fiction.
Early naturalists thought the unusual seeds came from strange underwater
plants whose origin was shrouded in mystery. In England sea hearts were
carried as good luck charms by sailors embarking on a long ocean voyage.
It was thought that if sea hearts could survive a long and perilous journey
across the ocean, perhaps they could also protect their owner. Christopher
Columbus was fascinated with objects that drifted ashore on beaches of the
Azores, off the coast of Portugal. It is said that a sea heart provided
inspiration to Christopher Columbus and led him to set forth in search of
new lands to the west. In fact, the sea heart is called "fava de Colom,"
or Columbus bean, by Portuguese residents of the Azores.

The Mary's Bean

Another drift seed called Mary's bean (Merremia discoidesperma) was a
special find to pious beachcombers. Named after the Virgin Mary, it is
also called crucifixion bean because of a cross etched on one side. The
distinctive seeds are produced in papery capsules on a climbing tropical
vine. The cross is actually an impression where the seed was attached
inside the capsule. Because of a thick, woody seed coat and internal air
cavities, the seeds are very buoyant and may drift for months or even years
at sea. Historically, the unique seeds have been used for good luck charms
and to ward off evil spirits. A woman in labor was assured an easy
delivery if she clenched a Mary's bean in her hand. Seeds were handed down
from mother to daughter as treasured keepsakes. To this day Mary's beans
are occasionally sold by street vendors in Costa Rica.

In its native habitat, the Mary's bean is known from only a few
locations in Mexico and Central America. It is a lovely vine of the
Morning Glory Family (Convolvulaceae) with beautiful yellow, funnel-shaped
blossoms. As drift seeds, the Mary's bean is known from the Marshall Islands to beaches of Norway, a total distance of more than 15,000
miles (24,000 km). According to Charles R. Gunn (Economic Botany Vol. 31, 1977), this
constitutes the widest drift range of any seed or fruit which has been
documented. Other pantropical drift seeds may drift as far or farther, but
their precise point of origin cannot be determined with certainty.

Large Neotropical Drift Fruits

With the exception of introduced
cattle, donkeys and horses, no native mammals of the New World tropics can crush the hard, thick-walled pods of many rain forest trees in their jaws. Livestock apparently like the sweet pulp inside the pods of West Indian locust (Hymenaea courbaril) and disperse the hard, viable seeds in their excrement. In areas without livestock, the rotting pods litter the
ground beneath large trees. Agoutis, tapirs and peccaries chew
open the rotting pods and eat the sweet pulp and seeds, but are not
major agents of seed dispersal like the larger hoofed mammals.
According to the authority on Central American rain forests, Daniel
H. Janzen (Science Vol. 215, 1982), large grazing mammals,
including extinct pleistocene elephants called gomphotheres, may
have once eaten the pods and dispersed the seeds in lowland
forests. In Africa, the large woody pods of related species are
quickly devoured by large herbivores. There are other Central
American rain forest trees that also appear to be missing their
natural herbivorous dispersal agents. Their hard, woody,
indehiscent fruits pile up beneath the branches and slowly rot away
in the soggy, moldy layer of soil and debris. The lack of natural dispersal agents may also apply to devil's claw pods that litter the ground in temperate regions of the New World.

The Manchineel Tree

There are dozens of unusual drift seeds that wash ashore on Caribbean islands, each with fascinating stories about them. One of the most interesting is an intricately-sculptured star that comes from the fruit of a native tree called the manchineel tree (Hippomane mancinella). The fruit of the manchineel tree resembles a small green apple, except this "apple" has a woody, seed bearing endocarp and is quite poisonous. Manchineel trees are common along Caribbean shores, and the fruits often fall into the water. The outer fleshy layer rots away and the buoyant, woody endocarp starts a new career as a drift disseminule. After many months of wave action and abrasion in tropical waters, the endocarp gradually becomes eroded into an intricate star. It is a beachcomber's delight to find one of these beautifully-sculptured stars.

Fruits of the manchineel tree (Hippomane mancinella) resemble small green apples. The seed-bearing pits (endocarps) float in tropical waters and gradually become eroded into intricately-sculptured stars.

The manchineel tree belongs to the diverse Euphorbia Family (Euphorbiaceae), and like many members of this family, it contains a poisonous milky-latex sap. The toxin is a mixture of diterpene esters, and contact with the skin may cause inflammation and a blistering rash. The caustic terpenes are structurally similar to phorbol, a potent carcinogen listed among organic compounds in the Merck Index. One of the earliest written accounts of the manchineel tree appeared in memoirs of Columbus' second voyage to the West Indies in 1493. On November 3 a landing party went ashore on the island of Marie Galante. The fleet physician, Dr. Chanca, writes: "There were wild fruits of various kinds, some of which our men, not very prudently, tasted; and upon only touching them with their tongues, their countenances became inflamed, and such great heat and pain followed, that they seemed to be mad, and were obliged to resort to refrigerants to cure themselves."

A young manchineel tree (Hippomane mancinella) that has sprouting in the sand of a Costa Rican beach. The beach was littered with the green, apple-like fruits of this ocean-dispersed species.

Sea Coconuts & Hand Grenade Pod

Two more interesting drift fruits that wash ashore along beaches of the Caribbean and the southeastern United States are sea coconut (Manicaria saccifera) and grenade pod (Sacoglottis amazonica). Both drift fruits come from trees that are native to the Amazon River, and are often carried by the Gulf Stream to beaches of Northern Europe. The sea coconut is a tall, unusual palm with leaves nearly 30 feet (8 meters) long. This palm has been listed by some authors as the longest undivided leaf of any plant; however, according to Chuck Hubbuch of Fairchild Tropical Garden, Coral Gables, Florida, the leaf is typically divided shallowly at the tip and is not truly entire. The tuberculate fruit wall contains one to three globose seeds which become sun-bleached and resemble golf balls strewn along beaches. This striking palm is more closely related to the coco-de-mer (Lodoicea maldivica) of the Seychelles Islands rather than the true coconut (Cocos nucifera).

A three-seeded fruit and two seed-bearing endocarps of the sea coconut (Manicaria saccifera), a palm native to the Amazon basin. Sometimes the tuberculate fruits contain only one or two seeds.

The buoyant fruits of grenade pod contain numerous hollow pockets which permit them to float for great distances. The raised pocket areas, which are exposed when the outer exocarp layer is eroded away, produce the faceted (bumpy) surface of the endocarp which superficially resembles a hand grenade. In Mexico these unusual fruits are often called "cojon de burro," a descriptive name that is probably not as appropriate as hand grenade. They are produced by a small tree native to the Amazon and Orinoco River basins of South America.

Two types of grenades: Fruits (endocarps) of the Amazonian tree Sacoglottis amazonica compared with a World War II hand grenade.

Like the migrations of ancient mariners, seafaring seeds have traveled to tropical beaches throughout the world. Collecting drift seeds can be a rewarding hobby--botanical treasures from exotic beaches to be admired for years to come. Some seeds (such as sea beans and sea hearts) can be polished in a stone tumbler, as you would polish agates and other precious stones, and different seeds can be strung together to make attractive necklaces and leis. Who knows--they might even bring you health and good fortune, like the fabulous tales from courageous explorers many centuries ago.